1. Field of the Invention
This invention concerns cyclic para-oriented aromatic amide (aramid) oligomers and the ring opening polymerization thereof and a process for preparing cyclic oligomers.
2. Technical Review
Aromatic polyamides (aramids) are generally synthesized by the reaction of an aromatic diacid chloride with an aromatic diamine in an appropriate solvent. Nomex.RTM. aramid (poly(m-phenylenediamine-m-phthalamide) and Kevlar.RTM. aramid (poly(p-phenylene-diamine-t-phthalamide) are two examples of products based on polymers prepared in this manner. Ring opening polymerization could simplify aramid polymerization processes versus "acid chloride plus amine" processes because no by products would be eliminated in the course of the polymerization reaction. Thus, no hydrogen chloride by product would be formed which would eliminate corrosion potential, a major concern with current aramid processes.
A necessary prerequisite to the practice of ring opening polymerization is a process route to cyclic oligomers of the monomers that are the components of the desired polymer. Cyclic oligomers and ring opening polymerization are known in a variety of polymeric systems, for example, aliphatic polyesters, silicones, epoxides, and a limited number of selected polyamides
T. L. Guggenheim et al., Polymer Preprints 30(2), 138 (1989), describe the synthesis of cyclic amide oligomers from diamines containing the spiro bis indane group reacted with isophthaloyl chloride and further report the copolymerization of this cyclic aramid oligomer with caprolactam. The authors further report that simpler diamines, e.g. m-phenylene diamine and 2,2-bis-(4-aminophenyl)propane, when reacted with isophthaloyl chloride or terephthaloyl chloride, afforded no appreciable amount of cyclic oligomer. Functional groups separated by para phenylene moities were believed to have a negative effect on cyclic oligomer formation.
Similar cyclic amide oligomers, all based on spiro bis indane derivatives, are described in U.S. Pat. Nos. 4,808,754, 4,837,298 and 4,868,279. U.S. Pat. No. 4,808,754 describes a process for the preparation of cyclic polyamide oligomers by the reaction of spirobiindane diamines, including spirobiindane bisphenol bisphenol dis-aminophenoxy ethers with dicarboxylic acid chloride. '754 claims certain spirobiindane bis-aminophenoxy ethers. U.S. Pat. No. 4,837,298 describes a process for preparing cyclic imides by the reaction of a bis(dicarboxyphenyl) sulfide or functional derivitive thereof with a diamine having a spirobiindane nucleus. U.S. Pat. No. 4,868,279 describes a spiro(bis)indane copolyamide and the preparation thereof by the reaction of monocyclic spiro(bis)indane polyamide oligomers with lactams in the presence of basic reagents.